This application relates to wireless communication systems and techniques that implement reuse of communication frequencies.
Wireless communication systems use electromagnetic waves to communicate with wireless communication devices located within radio cells of coverage areas of the systems. A radio spectral range or band designated or allocated for a wireless communication service or a particular class of wireless services may be divided into different radio carrier frequencies for generating different communication frequency channels. This use of different frequencies for different communication channels may be used in various multiple access radio wireless communication systems, e.g., frequency division multiple access (FDMA) systems and time division multiple access (TDMA) systems.
For a given wireless system, the communication capacity increases as the number of the communication frequency channels increases. For this and other reasons, the radio frequency is a valuable resource in such wireless communication systems. Unfortunately, two different frequency channels, when placed too close to each other in frequency, can interfere or cross talk with each other to create noise and thus reduce the signal-to-noise ratio. Hence, some system implementations impose a minimum frequency spacing between two adjacent channels to mitigate the adverse effect of the interference. Implementations of such a scheme can limit the number of frequency channels within a given radio spectral band. The minimum frequency spacing should be as small as possible in order to allow for as many channels as possible within a given spectral range.
One technique to reduce the minimum frequency spacing between two adjacent channels is to generate different channels within a given band by using the orthogonal frequency division multiplexing (OFDM) to generate channel spectral profiles that are orthogonal to one another without interference when different channels are centered at selected equally-spaced frequencies. Under the OFDM, the frequency spacing can be smaller than the minimum spacing in conventional channels and hence increase the number of channels within a given band. The existing and developing specifications under IEEE 806.16x standards support wireless communications under OFDM and orthogonal frequency division multiple access (OFDMA). The draft for IEEE 806.16d published in January 2004 provides technical specifications for OFDM and OFDMA wireless systems.
In OFDM, OFDMA and other wireless systems using channels at different frequencies, channel frequencies are generally strategically allocated to radio cells throughout the coverage regions. When properly allocated or planned, one or more channel frequencies may be reused in different radio cells that are spatially separated to reduce the interference below a tolerance level for that system. This frequency reuse is an important and integral part of the system design and can significantly affect the system capacity and the performance.